1. Field of the Invention
The present invention relates generally to a Multimedia Broadcast/Multicast Service (MBMS) service. In particular, the present invention relates to a method and apparatus for enabling partial combining of an MBMS service.
2. Description of the Related Art
Currently, with the development of communication technology, services provided by a wideband Code Division Multiple Access (CDMA) mobile communication system are evolving into packet service communication for transmitting not only the conventional voice service but also high-capacity data such as packet data and circuit data, and into multimedia broadcast/communication capable of transmitting multimedia services. In order to support the multimedia broadcast/communication, researches are being conducted on an MBMS service in which one or more multimedia data sources provide services to a plurality of user equipments (UEs).
The term “MBMS service” refers to a service for transmitting the same multimedia data to a plurality of users via a wireless network. The MBMS service enables the plurality of users to share one radio channel, thereby saving radio transmission resources. The MBMS service requires a large amount of transmission resources, as it supports transmission of multimedia data such as real-time image and voice, still image and text, and can simultaneously transmit voice data and image data according to the type of the multimedia data. In the MBMS service where the same data must be transmitted to a plurality of cells where the users are located, Point-to-Point (PtP) connection or Point-to-Multiple point (PtM) connection is achieved according to the number of the users located in each cell.
FIG. 1 is a diagram schematically illustrating nodes involved in an MBMS service in a mobile communication network.
Referring to FIG. 1, UEs 161, 162, 163, 171 and 172 mean terminal devices or subscribers capable of receiving the MBMS service, and a cell#1 160 and a cell#2 170 are logical or geographical areas where they wirelessly transmit MBMS-related data to their subscribers. The cell#1 160 and the cell#2 170 are controlled by the associated Node Bs. A radio network controller (RNC) 140 controls a plurality of the cells 160 and 170, selectively transmits multimedia data to a particular cell, and controls a radio channel established to provide the MBMS service. Connection between the RNC 140 and the UEs 161 through 172 is achieved through a radio resource control (RRC) interface.
The RNC 140 is connected to a packet switched or packet service (PS) network such as the Internet by a serving GPRS support node (SGSN) 130. Communication between the RNC 140 and the PS network is achieved by packet switched signaling (PS signaling). In particular, connection between the RNC 140 and the SGSN 130 is called an Iu-PS interface. The SGSN 130 controls an MBMS-related service for each of the subscribers. Typically, the SGSN 130 takes charge of managing service accounting-related data for each user and selectively transmitting multimedia data to a particular RNC 140.
A transmit network 120 provides a communication path between a broadcast multicast service center (BM-SC) 110 and the SGSN 130, and can be connected to an external network by a gateway GPRS support node (GGSN; not shown). The BM-SC 110, a source of MBMS data, takes charge of scheduling on the MBMS data.
In addition, the RNC 140 is connected to a circuit switched (CS) network (not shown) by a mobile switching center (MSC) 150. The CS network refers to an access-based voice-oriented legacy communication network. Communication between the RNC 140 and the MSC 150 is achieved by circuit switched signaling (CS signaling). In particular, an access between the RNC 140 and the MSC 150 is called an Iu-CS interface
An MBMS data stream is delivered to the UEs 161, 162, 163, 171 and 172 via the transmit network 120, the SGSN 130, the RNC 140 and the cells 160 and 170. Although not illustrated in FIG. 1, a plurality of SGSNs can exist for one MBMS service and a plurality of RNCs can exist for each of the SGSNs. Each of the SGSNs performs selective data transmission to its RNCs, and each of the RNCs performs selective data transmission to a plurality of its cells. To this end, each of the nodes stores therein a list (list of RNCs for the SGSN, and list of cells for the RNC) of nodes to which it must transmit the data stream, and later performs selective MBMS data transmission only to the nodes in the stored list.
In order for the MBMS data transmitted up to each of the cells to be successfully delivered to the UEs, several MBMS logical channels are used. Among the MBMS logical channels, an MBMS control channel (MCCH) carries MBMS control information including the type of an MBMS service provided in each cell, channel information, and MBMS information from neighboring cells, so that the UE can successfully receive the MBMS data. An MBMS traffic channel (MTCH) is a logical channel for carrying actual MBMS data. The MCCH and the MTCH, when transmitted on a PtM basis, are mapped to a forward access channel (FACH) which is a kind of a transport channel, and the FACH is mapped to a secondary common control physical channel (S-CCPCH) before being physically transmitted. In one cell, each MBMS service is generally mapped to different MTCHs, and the MTCHs can be mapped to one S-CCPCH by time division multiplexing (TDM). When several MBMS services are mapped to one S-CCPCH, the UE unnecessarily wastes power in receiving undesired service.
In order to solve the problem, the 3rd Generation Partnership Project (3GPP) group defines a logical channel called an MBMS scheduling channel (MSCH), being mapped to the S-CCPCH, and includes, in the MSCH, scheduling information for MBMS services included in the S-CCPCH such that the UE can selectively receive desired service.
Generally, the WCDMA system can achieve a gain in terms of utilization of transmission power and radio resources by combining the same-content data transmitted from different cells, and this can be applied even to the MBMS service. If one physical channel is equal in content to a physical channel transmitted from another cell, the physical channels received from two cells can be combined with each other at anytime. This combining is called “full combining.” However, if data on the two channels is partially equal, only the same part can be combined, and this is called “partial combining.”
In the case of the MBMS service, because S-CCPCHs transmitted from a plurality of cells undergo different scheduling, the UE must partial-combine only the data in the period where its interested service is located among MBMS services included in the S-CCPCHs. Therefore, the different S-CCPCHs transmitted from the plurality of cells require a method for efficiently performing partial combining according to the corresponding scheduling.